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Re: Frame chimney height and potential support

good question Ross, for masonry chimneys they mention shear design, but for wood framed with siding you would cross referance plywood fastening ,blocking for walls over ten feet ,ect and you would hope the designer or framer maybe ran 2x6 studs 22' footers lapped up the walls and into the air to help stiff back it a little.

Was there any stress signs at the step flashing along the cricket from the wind rocking it or did the chimney frame look like it was leaning or did the siding looked distorted or even seperated any where from wind loads against it. Unless the chimney cap is failing or the step flashing looks not installed correctly then in my opinion theres nothing to report structurally,

i know a lot of chimneys standing framed with the studs up with the first floor plate line and then another elevation of studs up to the finish hieght and you can feel the frame move, but never worried it would topple

Re: Frame chimney height and potential support

Not aware of a specific requirement for bracing but I get around that easily. I push on it from the sides and see if it moves. They usually do when that tall. Once I put in the report that 'the chimney enclosure moved with minimal force exerted against it', nobody cares what's required, they want it braced.
The other important factor, and I don't recommend anyone do this, is that if the structure feels solid enough I put my ladder against it and go to the top to get a pic of the opening. Whenever the top is framed flat, chances are its open around the pipe, rotted/rusted out, water leaking in and needs repair. The pic is usually pretty ugly so getting people to cooperate tends to be easy. Seller is usually pissed their contractor screwed them.

www.aic-chicago.com
773/844-4AIC"The Code is not a ceiling to reach but a floor to work up from"

Re: Frame chimney height and potential support

Interesting. First question I'd ask, is there a current problem with chimney (i.e. rot, movement or noise in the wind). How long has this been here? What are local wind conditions? If it were the Oregon coast it wouldn't be built. Structurally it may be adequate, in that it's continuous thru the roof and supported by the lower story wall, AND is sheathed for shear resistance (I'd be satified with 1/2" plywd glued and screwed - box girder fashion). If client is worried, recommend builder to remove cap and check out the construction if they don't have the as-builts.

Re: Frame chimney height and potential support

A big question to ask is, "what condition is the chase cover in?" Next time you have your chimney swept, ask the Sweep what to top looks like. If it's rusted, it may be time to replace the cap with a new one, preferably one made of Stainless Steel so it won't rust out again, and cross brakes to ensure it won't sag and puddle water! The Sweep should also check to make sure the caulking around the storm collar is water-tight.

Water penetration can cause a lot of unseen damage in a chase like that which would be visible from outside.

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